Stylus Drag

The problem I envisage with the timeline is that if there is a regular (emphasis on regular) slowing down and speeding up of the platter between flashes the timeline will show perfect speed where the reality in realtime will be very different....a bit like the teacher who checks on a class every 2 minutes and sees a class of perfect angels but as soon as he/she goes out of the room the kids start running amok.
I like the idea of the Feickert app better BUT, in playing a steady tone on the test disc there is no way to really test differences in groove modulation and it's effect on stylus drag.
An experiment for those of you with multi-arm tables would be to play an LP with heavily modulated grooves with one arm and then have the 7" (3150Hz tone) Feickert disc sitting on top of the LP being played at the same time by the other arm. Obviously with only the test tone selected to play through the speakers using the app you could see the exact effects of stylus drag in realtime.
My own observation is that a centre hole that is even a tiny bit off centre (most records and IME especially modern 'audiophile' repressings) will cause audible pitch variations that totally SWAMP inherent differences between turntables. In testing my own turntables(both belt and direct drive)with the Feickert app this was certainly the case.

The fact that a platter slows when the stylus is in the groove is not the same as what as referred to as stylus drag.

That is how I define stylus drag. What else would it be??

Stylus drag is defined by the coefficient of friction between the stylus and the vinyl groove multiplied by the normal force (tracking force) of the stylus. I found some old technical papers that measured and evaluated the coefficient of friction of vinyl records comparing different vinyls as well as cleaners and lubricants. Surprisingly, the coefficient of friction can vary quite a bit. They showed numbers ranging from 0.2 to 0.4. Multiply that by your tracking force, eg. 2 grams and the stylus drag can range from 0.4 to 0.8 grams. That drag is what generates the skating force component on the tonearm. So your anti-skating setting is an indicator of just how much stylus drag you have- less bearing friction in your tonearm. As an aside, if your tt sounds better with no anti-skating applied, then perhaps the tonearm bearing has some significant friction.
As for speed control: I have shown some calculations in other threads for information and inspiration purposes. Observations with the timeline show that the speed shifts on some tt's when the needle is dropped onto the record. That doesn't mean it is a bad tt. Any external force applied to a platter must be reacted to by the motor/speed control system. Dropping the needle onto the record can add about 0.011-0.021 in-lbf (120-240 g-mm) of torque to the platter. How much that changes the speed, if any is dependent entirely on the tt.
So let's say someone using the timeline with a 500mm radius to the wall observes a 2mm shift in the red line when they drop the needle onto the record. At 500mm that is a 0.06% change or 0.02 rpm shift. If you were playing a 3150Hz test tone, that would cause a 1.9Hz change. Now what I thought I read was that the red line on the wall shifted one time as the needle hit the record but then did not drift while playing the record. What is wrong with that? So the speed shifted ever so slightly due to the torque change. The motor/control system compensated and the record platter speed remained stable afterward. Seems fine to me. The timeline accuracy is good to three decimal places and almost all turntables are good out to two decimal places. Record runout is good only to one decimal place. Ref my calculations in the other thread. I can hear record runout. That is the real problem. I cannot hear my turntable's 0.02%/0.03% Wow and Flutter- not even in the soundstage or other subtle cues. And my analog soundstage is superior to CD.

Tonywinsc,

Good stuff! Thanks for adding some well thought out metrics to the discussion!

If any specific turntable is able to maintain speed adequately when a record of mass N (N would vary from record to record) is placed on the platter, isn't it reasonable to think that adjusting for stylus drag as well once that comes into play as well is not a problem?

As far as stylus drag's affect on speed control, let me also explain that platter mass is part of the entire speed control system. The speed control system is designed around the motor and platter inertia. Turntable designers, especially belt drive tt's use platter mass for dampening. Mass is commonly used for dampening. Your car engine and even your car body has mass dampers to minimize the vibrations that you feel and hear in the car. A massive platter requires more torque to control speed- and so belt drive tables use the small motor pulley and large platter outside diameter as a torque multiplier. A direct drive tt has a relatively low mass platter and as many on this forum will attest, also has excellent speed control. The speed control system is different for the low mass DD tables as compared to a belt drive table. DD turntables simply use a different control system for the lower inertia platter. DD turntables were originally designed for DJs so they could stop/start the platter quickly. My personal preference is the massive platter on a belt drive table because the mass doesn't just dampen torque variations, but also external vibrations from the floor and the air. The massive platter makes a great sink for the record. DD turntable users have to admit that they must work hard to isolate their DD turntables and platters from vibrations.